Preparation of caustic liquor



March 7, 1933.. M, B, MOUNT PREPARATION oF cAUsTIc LIQUoR Filed Nov. ll,1930 INVENTOR W, m W

mw* n ATTORNEY Patented Mar. 7, V1933 PATENT OFFICE MORRIS BLAKE MOUNT,0F LYLIGHBURG, VIRGINIA PREPARATION rOF CAUSTIC LIQUOR Application ledNovember il, 1930. .Serial No. 494,915.5

vHeietofore, there have been two processes for the preparation ofcaustic liquor incommon use, the batch process and the continuousprocess.

5 A that is, the batch process, the liquor ismade in quantities orbatches. AThe operation Yofthe batch process is necessarilyintermittent, but its appeal lies in its simplicity, which permits' Tthe operation of the process with the mini- 0 mum amount of attentionfrom the operators.

' tinuous process, all of the operations proceed at a delinite rate, thematerials enteringv one end and the caustic liquor and sludge beingWithdrawn at the opposite end. Both of these processes areYfundamentally1 thev same in that liquor is causti'cized and the caus-.tic liquor produced is clarified. The 'clarification of thecaustic'liquor consists in separating the sludge and the liquor,A and itisj commonly accomplished by decantation The sludge remaining after thecaustic liquor is decanted, contains a considerable quantity of strongcaustic liquor which in existing systems is diluted with Wash water usedto recover the alkali remaining in the sludge, and

it is to a process for the preparation of caustic liquor in which anincreased yieldV of y in g much ofthe caustic liquor in thesludge asstrong caustic liquor, that my invention relates. l p

By the process of my invention I obtain a considerably greaterpercentage of the total volume of liquor causticized as strong causticliquor. I obtain this increased yield of strong caustic liquor byiiltering the sludge which remains after decanting the clear causticliquor. The sludge is filtered without t; the addition of wash Ywater,softhat strong In the first of these processes,

In the latter process, namely, the con- .continuously filtered, as,lforexample, in a Vcontinuous filter.

strong caustic liquor is obtained by .recover` tus shown there in is, inthe main, standard and eliiciency of the continuous process. The entireprocess is carried on in aclosed cycle which greatly reduces the alkalilosses. y vIncombining the batch yand continuous processes,lime isslaked, in successive batches, in a mixing and slaking tank withpredeterv mined volumes of sodium carbonate solution and weak filtratewhich in the closed `cycle isreturned to this tank, as will-hereinafterappear. The mixture is agitated `d uringthe G0 slaking of the lime. `Thecarbonate and milk of lime mixture formed in the slaking tank isthencausticized. kSuccessive batchesV ,of caustic liquor and'sludgeare-delivered to a storage or pumping-tank whereinthe mixture of thecaustic liquor'and the sludge is vcontinuously agitated to maintain thesludge in suspension. From the pumping tank, the mixture of causticliquor and sludgeis continuously withdrawn and delivered to acontinuousdecanter wherein the sludge settles and clear caustic liquor is decantedand sent vrto* storage.k The sludge is continuously removed from thedecanter as it settles and is 75 The filtrate obtained from l thisfiltering-of the sludge is strong caustic liquor and is returned to thedecanter where any sediment containedy therein is removed therefrom. Thecake formed on-the continuous lilter is washed with washing .water anddelivered to a resludger wherefit is re-. pulped with-, water. Therepulped sludge is lagain filtered, a-weak filtratebeing obtained. Thisweak filtrate is delivered to the slaking tank where it is usedinslaking the lime.

f Ivshall now describe the embodimentot the apparatus shown vin theaccompanying drawing vfor carrying out my.r process, in which the singlefigure diagrammaticallyrepresents'the arrangement of theapparatus. `Theapparatus shown in the drawing is illustrated diagrammatically as theapparal equipment inthe alkali industry, andthe 'i novelty residesinthecombination andarrangementy thereof. Lime is silaked in the mixingand slaking tank 1 with predetermined volumes of a carbonate solutionand sludge in suspension.

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weak filtrate or wash water. The weak filtrate is introduced through aninlet 2 which is connected to a conduit 3 through which the weakfiltrate or wash water for slaking the lime is delivered. from a weakfiltrate storage tank t. rEhe tank is of a type well known in the alkaliindustry and is equipped with a perforated plate on to which the mixtureof lime is dumped. All of the linie which passes through theperforations in the plate is carried through the system. The tank 1 isalso equipped with a low speed agitator for agitating the mixture in thetank, and a drag for reducing lumps of lime so that they will passthrough the perforations in the plate onto which the lime is dumped.When the desired strength of the milk of' lime mixture has beenobtained, the charge is withdrawn through an outlet 6 by a pump 7 and isdelivered through a conduit 8 to a reaction tank 9 where causticizationis completed.

vrllhe reaction tank is completely enclosed and is equipped with a highspeed agitator so that a positive and thorough mixing of the chemicalsis obtained. ln addition to being thoroughly agitated in the reactiontank, the milk ofv lime' mixture delivered thereto is heated, preferablyby steam. The agitation of the mixture during the causticization in thereaction tank is a very important feature and `for this reason theagitation should be positive and thorough. 1t is a known fact thatwithsuitable agitation in the reaction tank, the steam used in heating themixture `may be confined to the amount required to raise the charge tothe boiling point and maintain it at that temperature during thereaction period and an increased conversion to caustic liquor will beobtained.

1n the reaction tank shown, the mixture is continuously agitated for asuitable period, approximately twenty or thirty minutes, and is thendelivered through a conduit 10 to a storage or pumping tank 11. Thereaction tank may be located at a higher level than the pumping tank inwhich case the liquor would flow through the conduit 10 under the actionof gravity. The pumping tank is equipped with a low speed agitatorVwhich agit-etes the mixture therein to maintain the The liquor with thesludge in suspension is continuously withdrawn from the pumping tankthrough an outlet 12 by a pump 13 and delivered through a conduit 14 tothe central well 15 of a continuous decanter 16. The rate at which thecausticized liquor and sludge is delivered to the decanter is determinedby the total volume to be handled in a given period of time.

A continuous separation of the clear caustic'liquor and the sludge isobtained in the v continuous decanter. The clear caustic liquoroverflows into a launder 17 surrounding the top rim of the decanter fromwhence itis withdrawn and delivered to the caustic liquor storage. rlhesludge settles to the bottom of the decanter and flows under the actionof the force of gravity through the conduit 18 to a sludge supply tank19 which is equipped with a low speed agitator.

rThe sludge withdrawn from the continuous decanter is undiluted and theconsistency of the sludge is approximately 25% solids and strong causticliquor by volume, and represents 45 to 50% of the total volume of liquorcausticized. The ratio of the solids to the liquor in the sludgewithdrawn from the continuous decanter may be controlled within deiinitepredetermined limits.

From the sludge supply tank, the Sludge is withdrawn through an outlet20 by a pump 21 and delivered through a conduit22 to a primary filter23. rllhe sludge is pumped at a continuous rate to this filter which isa continuous filter of the compartment type. r1`he filter is equippedwith an overflow which is connected to the sludge supply tank by meansof a conduit 24. Thus, any sludge overflowing the filter will bereturned to the sludge supply tank. Although any suitable type of filtermay be used 1 prefer to use the continuous, compartment type rotaryvacuum filter, such as that which forms the subject matter of mycopending application Serial No.

505,509 filed Dec. 80, 1930. With this type of filter undiluted causticliquor may Vbe drawn through Yeach compartment during that portion ofeach revolution of the drum in which the compartment is submerged andwash water may be supplied to the sludge on the filter during eachrevolution et the drum, the weak filtrate being withdrawn through thecompartments during that portion of each revolution of the drum in whichthe compartment is not submerged. The filtrate obtained through thesubmerged portion of the filter drum is undiluted and is the strongcaustic liquor carried by the sludge. This filtrate is withdrawn througha conduit 25 by means of a vacuum pump 26 which is connected to theconduit 25 through a trap 27. ln the trap 27, the strong ltrate isprevented from passing through the trap to the vacuum pump. The strongFiltrate is withdrawn from the trap 27 through a conduit 28 by means ofa pump 29 and is delivered through a conduit 30 to the central well 15oi the continuous decanter where any small amount of proximately 20 to25% over the processes heretofore in use.

.is connected through a weak filtrate trap 32 to the vacuum pump 26. e

Following the preliminary washing on the upper portion of the primaryfilter drum the cake is repulped with hot water in a resludger 33 fromwhich it is withdrawn and delivered through aconduit 34 tok a secondaryfilter 35 whereit is given a final washing. lThe weak filtrate from thissecondary -filter is withdrawn througha conduit 36 whichis con- .inected to the conduit 31 through which the weak filtrate from theprimary filter is delivered to theweak filtrate trap 32. The weak yzo.ltrate uis withdrawn from the trapv 32 through a conduit 37 by a pump38 and delivered through a conduit 39 to the weak filtrate storage tank4 Jfrom which it is withdrawn as needed to be used'in the slaking oflime in the .mixing andslaking tank l..

'located directly over the feed end of thekiln. 35 Y The processdescribed in detail. above permits a posltlve control over the slakingoperation and the preparationof av milk of lime -mixture that ischemically and physically suited to the'V causticizingA operation; itper,-

mits ahigh` degree of control over causticity; it permits achemicalcontrol throughout the process of a type that can be exercisedby the operatives in chargewith a'minimum amount of supervision; and, itprovides a vpositive circulation of the material-in the reaction tank.In the process, there is a greatly decreased steam consumption; theamount of core thatV must be removed from the slaking tank is materiallyreduced; there is a continuous and thorough settling of the sludge andaminimum alkali lossin the discarded sludge. The cycle described is aclosed cycle and therefore eliminates the possibility of losing chargesof the liquor through carelessness of the operators. Thesystem also hasthe advantage in that there is a minimumhandling of chemicals; a minimumdilution'of chemicals; and

a low cost of installation and operation, coupled with a. recovery ofover '70 to 75% of the Vtotal volume of liquor causticized.

It will be obvious that various changes may be made in the steps of myprocess and the apparatus described immediately above within theprinciple and scope of my 'invention as expressed in the appendedclaims.

' line I claim:

1. The process for the preparation! of causticliquor which consists intreating successive batches of liquor containing soda 'ash by slakinglime therein, causticizing the milk of lime mixture, delivering thesuccessive batches of the causticized milk of lime mix- ,ture and sludgeto a tank, continuously withdrawing the liquor andsludge from y,the tankand delivering it to a continuous decanter, and continuously decantingthe clear caustic liquor.

2. The process for the preparation of causticl liquorwhich consists intreating `successive batchesof liquor containing soda ash-by slakinglime therein, causticizing the milk of mixture, delivering thesuccessive batches of caustic liquorl and sludge to a storagetank,vcontinuously withdrawing the liquor-and sludge from lthe storagetank and delivering it to a continuous decanter,"'con tinuo'uslydecanting the clearv caustic liquor, continuously removing the sludgefrom the decanter, filtering the sludge as itv comes from the decanter,-and eliminating the sediment in the'filtrate to obtain clear causticliquor. 3.. The process for the preparation of caus- -tic liquor whichconsists in treating successive batches of liquor containing soda ash byslaking lime therein, causticizing the milk oflime mixture, deliveringYthe successive Y batches of caustic-liquor and sludge to a tank,lcontinuously withdrawing the liquor and sludge from the tank anddelivering it to a continuous deca'nter, continuously ydecanting theclear caustic liquor, continuously removing the sludge from thedecanter, and filtering the sludge removed from therdecanter.l Y

4. The process `for the preparation of caustic liquor which consists intreating successive batchesof liquor' containing soda ash by l slakinglime therein, causticizing the milk of hme mixture, delivering thesuccesslve batches of caustic liquor and sludge to a storage tank,continuously withdrawing the liquor and sludge from the storage tank and.delivering it `to a .continuous decanter,- continuously decanting theclear caustlc'hquo'r,

continuously7 removing the sludge from the deca'nter, filtering theysludge asv ity comes from the decanter, eliminating the sediment in thefiltrate to obtain lclear caustic liquor,

washing'the sludge removed by the filter, and y f i filtering the washwater from the sludge'.y 5. The process for the preparation of causticliquor which consists in treatin'gsuccesl.sive batches of liquorcontaining sodajashby slaking lime therein, causticizing the mil of limemixture,delivering thel successive batches vof caustic liquor andsludgev to a tank, continuously withdrawing the? liquor and sludge fromlthe tank and delivering it@ y to afcontinuous decanter, continuously de-`canting the clear caustic liquor, continuous- CTL ly removing thesludge from the decanter, filtering thesludge removed from the de-Ganter, and returning the filtrate to the decanter,

6..'l`he process for the preparation of causticv liquor' which consistsin treating successive batches of liquor containing sod-a ash by slakinglime therein, causticizin g the milk of lime mixture,rdelivering thesuccessive batches of caustic liquor and sludge to a storage tank,continuously withdrawing the liquor and sludge from the storage tank anddelivering it to a continuous decanter, continuously decanting theclearl caustic liquor, continuously removing the sludge from thedecanter, filtering the sludge as it comesfrom he decanter, eliminatingthe sediment in the filtrate to obtain clear caustic liquor, washing thesludge remove-dv by the filter, filtering the wash water from thesludge, and using the filtered Wash water in the slaking of the lime. 7.The process for the preparation of caustic liquor which consists intreating successive batches of liquor containingsoda ash by slaking limetherein, causticizing the milk of lime mixture, delivering thesuccessive batches of caustic liquor' and sludge to a tank, continuouslywithdrawing the liquor and sludge from the tank .and delivering it to acontinuous decanter, continuouslydecanting the clear ycaustic liquor,continuously removing the sludge from the `decanter, filtering theslu-dge removed from the decanter, returning the filtrate to thedecanter, washing the sludge removed by the filteriilter ing the washingwater from the sludge, and using the filter-ed washing water for theslak ing lof lime. v y

8. The process for the preparation of caustic liquor which consists intreating successive batches of liquor containing soda ash by slakinglime therein, agitating thelilquor during the slaking of the lime,causticizing the soda ash in the milk of'r lime mixture formed byslaking the lime in the liquor containing the soda ash, continu-allyagitating the milk of lime mixture during the causticization thereof,delivering the successive batches of caustic liquor and sludge to atank, agitating the caustic liquor in the tank to maintain the sludge insuspension, continuously withdrawing the liquor and sludge from the tankand delivering it to a continuous decanter, continuously decanting theclear caustic liquor, continuously removing the sludge from thedecanter, filtering the sludge removed from the decanter, and returningthe filtrate tothe decanter.

9. The process Vfor the preparation of caustic liquor which. consists intreating successive batches of liquor containing soda ash by slakinglime therein, agitating the liquor during the slaking of the lime,causticizing the soda ash in the milk .of lime mixture formed by slakingthe lime in the liquor sludge removed from thefilter, filtering thewashing water from the sludge, and mixing` the washing water with theliquor containing the soda ash during the slaking of lime.

l0. ln a process for the preparation of a caustic liquor, the stepsconsisting of continuously separating the caustic liquor from thecaustic sludge by decantation in a continuous decanter, continuouslyremoving the sludge from the decanter, filtering the sludge as itisremoved from the decanter, and elimin Y Y nating the sediment in thefiltrate.V

ll. ln the process for the preparation cfa caustic liquor, the stepsconsisting of continuously separating the caustic liquor from thecaustic sludge by decantation in a continuous decanter, continuouslyremoving the f sludge from the decanter, filtering the sludge removedfrom the decanter, and returning the filtrate to the decanter.

l2. ln the process for the preparationof a caustic liquor, the stepsconsisting of continuously separating the caustic liquor from thecaustic sludge by decantation in a continuous decanter, continuouslyremoving the sludge from the decanter, filtering the sludge removed fromthe decanter, returning the filtrate to the decanter, washing'y thesludge removed by the lter, filtering the washing water from the sludge,and using the washing Water for slaking lime.

In witness whereof, I hereunto subscribe my signature.

MORRIS BLAKE MOUNT.

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